The prior art includes a number of chemical dispensers for industrial dishwashers, including those disclosed in U.S. Pat. Nos. 4,509,543 (Livingston et al., 1985); 2,850,760 (Borell, 1955); 3,896,827 (Robinson, 1975); 4,142,539 (Shih et al., 1979); and 4,245,309 (Keifer, 1981).
The present invention addresses three shortcomings of the aforementioned prior art: the need for a better mechanism to set and control the concentration of detergent used in the wash water; the need for a better mechanism for detecting the failure of the system to add detergent to the wash water; and the waste of rinse agent and detergent in batch type industrial dishwashers.
A number of the prior art industrial dishwashers known to the inventors include a detergent level setting mechanism for setting the concentration of detergent to be maintained by the dishwasher in the wash water. In order dishwashers this level was generally either fixed or the amount of detergent used was determined by any one of a number of procedures that did not involve comparing the actual detergent concentration with a target concentration value.
In those prior art dishwashers known to the inventors which include a detergent concentration level setting mechanism, these mechanisms are "linear" in that the level specified by the user is linearly related to either the conductivity or resistivity of the wash water when the desired concentration of detergent is in the water.
These prior art detergent dispenser control mechanisms have always been somewhat unsatisfactory due to the lack of a natural or "user friendly" scaling or calibration scheme for the controller. That is, although dish water conductivity is approximately proportional to detergent concentration, the prior art detergent target level control mechanisms could not be scaled or calibrated in terms of a convenient unit such as tablespoons of detergent per gallon of wash water. Thus the numeric units, if any, on the detergent level controller tended to be arbitrary and are different on each brand of controller. As a result, the setting of the detergent level controller has generally been a trial and error procedure where the user selects a level and then adjusts the control dial up and down until an acceptable detergent level is observed. Typically the user overadjusts the control dial at least once during this procedure because of the lack of a suitable calibration scale.
During the last decade or so there prior art detergent level control mechanisms have become even less satisfactory due to two developments: the use of detergents with lower alkalinity levels and the trend toward using lower concentration levels of detergent. As a result of these developments a much broader range of detergents is being used by various dishwasher owners and the corresponding range of target conductivity or resistivity has also expanded. In particular, different users need accurate concentration control in different conductivity ranges.
The present invention solves the problem of providing a detergent level control mechanism which is accurate over a wide range of concentration levels and which provides a user friendly calibration or scaling mechanism. The problem is solved by providing a detergent level control mechanism which is scaled in logarithmic units. In particular, each unit measurement on the detergent level control corresponds to a preselected percentage change in detergent concentration. For instance, in the preferred embodiment each increment in the target detergent concentration level corresponds to approximately a five percent increase in the target conductivity of the wash water, which corresponds approximately to a five percent increase in detergent concentration.
The second problem referred to above is the inadequacy of prior art detergent dispenser control mechanisms which detect the failure of the dispenser to add detergent (which is usually caused by exhaustion of the detergent supply, but can also be caused by disconnection of the detergent supply hose and other such problems) by detecting the failure of the detergent to reach the target level within a specified amount of time. In some prior art devices the length of the time period used for this purpose can be selected by the user through the use of a calibrated dial. Typically the period of time used is at least two minutes long.
This detergent feeding failure detection mechanism is unsatisfactory for at least two reasons. First, if the failure is caused by a disconnection of the detergent feeding hose, a large quantity of detergent may be wasted before the control mechanism stops the detergent pump and issues a warning. Second, in batch type dishwashers the wash cycle is often only 45 seconds or so long and thus is too short for these type of mechanisms to detect a detergent feeding failure.
The present invention solves the above described problem by providing a mechanism which is sensitive to changes in the concentration of detergent in the wash water and which detects the failure of that concentration level to change. In the preferred embodiment, if the detergent concentration level does not increase by at least a certain predefined amount during a twelve second period in which the detergent dispenser is turned on, a detergent feeding failure alarm is generated.
The third problem addressed by the present invention is that the prior art dishwasher controllers known to the inventors do not distinguish between batch and conveyor type dishwashers. As a result, these prior art dishwasher controllers (1) allow rinse agent to be added to the rinse water through the full rinse cycle; and (2) allow detergent to be added to the wash during the rinse cycle.
Rinse agent facilitates the sheeting of water from dishes and thereby decreases spotting. In general, rinse agent can be saved without significant loss of sheeting action by using rinse agent only during the end of the rinse cycle.
Detergent should not be added to the wash water in batch type dishwashers during the rinse cycle because the lack of dish water agitation during the rinse cycle often results in the use of excessive amounts of detergent. More specifically, the wash water pump does not operate during the rinse cycle in batch type dishwashers. As a result, newly added detergent mixes poorly with the wash water during the rinse cycle. Therefore the measured detergent concentration will not reflect the amount of detergent actually in the wash tank and more detergent may be added to the wash tank than is needed to achieve the target concentration level.
In conveyor type dishwashers the continuous feeding of rinse agent is reasonable since new racks of dishes keep passing through the rinse section of the machine and therefore it is difficult to identify the end of the rinse cycle for each rack of dishes. In batch type dishwashers, however, the timing of the rinse cycle for each rack of dishes is known since only one set of dishes is being washed at a time. Similarly, in conveyor type dishwashers it is reasonable to enable the adding of detergent to the wash tank whenever the dishwasher is on because the wash water pump will always be on, thereby ensuring proper mixing of the detergent as it is added to the wash tank.
The present invention solves the above discussed problem by providing a switch for identifying the type of dishwasher attached to the rinse agent dispenser, a timer control mechanism for controlling the portion of the rinse cycle in which rinse agent is used, and a control strategy which prevents the addition of detergent to the wash water during rinse cycles in batch type dishwashers.
These and other features and advantages of the present invention are discussed more fully in the detailed description of the preferred embodiment.
It is therefore a primary object of the present invention to provide an improved industrial dishwasher chemical dispenser controller.
While the present invention concerns a dishwasher chemical dispenser and its controller, for convenience the term "dishwasher controller" is used herein synonymously with the term "dishwasher chemical dispenser controller". Therefore the term "dishwasher controller" is not used herein to mean a dishwasher sequence controller (such as item 46 in FIG. 1), except to the extent that a single, integrated control system provides both dishwasher sequence and chemical dispensing control features.
Another object of the present invention is to provide a dishwasher controller which includes a logarithmically scaled detergent level control mechanism.
Yet another object of the present invention is to provide a dishwasher controller which detects a detergent feeding failure by monitoring changes in the concentration of detergent in the dishwasher's wash water.
Still another object of the present invention is to provide a dishwasher controller with means for limiting the use of rinse agent to a preselected portion of the rinse cycle.